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Common Shares (Tables) | 12 Months Ended
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Dec. 31, 2020
Share Capital, Reserves And Other Equity Interest [Abstract] |
Issued and outstanding | TransAlta is authorized to issue an unlimited number of voting common shares without nominal or par value.
As at Dec. 31 | 2020 | 2019
| Common shares (millions) | Amount | Common shares (millions) | Amount
Issued and outstanding, beginning of year | 277.0 |  | 2,978 |  | 284.6 |  | 3,059 |
Purchased and cancelled under the NCIB | (7.3) |  | (79) |  | (7.7) |  | (83) |
Effects of share-based payment plans | — |  | (3) |  | — |  | — |
Stock options exercised | 0.1 |  | — |  | 0.1 |  | 2 |
Issued and outstanding, end of year | 269.8 |  | 2,896 |  | 277.0 |  | 2,978 |
The following are the effects of the Corporation's purchase and cancellation of the common shares during the year:
For the year ended Dec. 31 | 2020 | 2019
Total shares purchased(1) | 7,352,600 |  | 7,716,300 |
Average purchase price per share | $ | 8.33 |  | $ | 8.80 |
Total cost | 61 |  | 68 |
Weighted average book value of shares cancelled | 79 |  | 83 |
Amount recorded in deficit | 18 |  | 15 |
(1) As at Dec. 31, 2020, includes 456,200 (2019 -189,900) shares that were repurchased but were not cancelled due to timing differences between the transaction date and settlement date. All preferred shares issued and outstanding are non-voting cumulative redeemable fixed or floating rate first preferred shares.
As at Dec. 31 | 2020 | 2019
Series | Number of shares (millions) | Amount | Number of shares (millions) | Amount
Series A | 10.2 |  | 248 |  | 10.2 |  | 248 |
Series B | 1.8 |  | 45 |  | 1.8 |  | 45 |
Series C | 11.0 |  | 269 |  | 11.0 |  | 269 |
Series E | 9.0 |  | 219 |  | 9.0 |  | 219 |
Series G | 6.6 |  | 161 |  | 6.6 |  | 161 |
Issued and outstanding, end of year | 38.6 |  | 942 |  | 38.6 |  | 942 |
Earnings per share |
Year ended Dec. 31 | 2020 | 2019 | 2018
Net earnings (loss) attributable to common shareholders | (336) |  | 52 |  | (248) |
Basic and diluted weighted average number of common shares outstanding (millions) | 275 |  | 283 |  | 287 |
Net earnings (loss) per share attributable to common shareholders, basic and diluted | (1.22) |  | 0.18 |  | (0.86) |

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